Be() throws System.FormatException when expected value contains "{" #3147
Description
Description
Hi,
I was writing tests for my code formatter and came across this weird behavior - FluentAssertions use string.Format without sanitizing the values (but that is not optimal solution IMHO).
It is kind of annoying:
This works just fine:
// Ok
[Fact]
public void FormatParameters_MultpleParameters_MovedParametersToTheirOwnLines()
{
_formatter.Format("""
codeunit 0 C
{
procedure Nop(X: Integer; Y: Integer; Z: Integer)
begin
end;
}
""").Should().Be("""
codeunit 0 C
{
procedure Nop(
X: Integer;
Y: Integer;
Z: Integer)
begin
end;
}
""");
}This throws throws System.FormatException.
[Fact]
public void FormatParameters_MultipleParameters_ShrinksUnnecessaryWhitespace()
{
_formatter.Format("""
codeunit 0 C
{
procedure Nop(
// X
X: Integer;
// Y
Y: Integer;
// Z
Z: Integer)
begin
end;
}
""").Should().Be("""
codeunit 0 C
{
procedure Nop(
// X
X: Integer;
// Y
Y: Integer;
// Z
Z: Integer)
begin
end;
}
""";
}Thanks
Reproduction Steps
using FluentAssertions;
using Xunit.Sdk;
namespace DemonCore.Tests;
public class DemonCoreTests
{
[Fact]
public void NotOk()
{
DemonCore(80).Should().Throw<XunitException>(); // Be() throws System.FormatException
}
[Fact]
public void Ok()
{
DemonCore(79).Should().Throw<XunitException>(); // Be() does not throw but fails to format something.
/*
Actual assertion message if we just run `DemonCore(79)();`.
**WARNING** failure message 'Expected actual to be a match with the expectation, but it differs at index 0:
↓ (actual)
"{xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"
""
↑ (expected)' could not be formatted with string.Format
at System.Text.ValueStringBuilder.AppendFormatHelper(IFormatProvider provider, String format, ReadOnlySpan`1 args)
at System.String.FormatHelper(IFormatProvider provider, String format, ReadOnlySpan`1 args)
at System.String.Format(IFormatProvider provider, String format, Object[] args)
at FluentAssertions.Execution.FailureMessageFormatter.FormatArgumentPlaceholders(String failureMessage, Object[] failureArgs)
*/
}
private static Action DemonCore(int number) =>
() =>
{
var actual = "{" + new string('x', number);
var expected = "";
actual.Should().Be(expected);
};
}<Project Sdk="Microsoft.NET.Sdk">
<PropertyGroup>
<TargetFramework>net10.0</TargetFramework>
<ImplicitUsings>enable</ImplicitUsings>
<Nullable>enable</Nullable>
<IsPackable>false</IsPackable>
</PropertyGroup>
<ItemGroup>
<PackageReference Include="coverlet.collector" Version="6.0.4" />
<PackageReference Include="FluentAssertions" Version="8.8.0" />
<PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.0.1" />
<PackageReference Include="xunit" Version="2.9.3" />
<PackageReference Include="xunit.runner.visualstudio" Version="3.1.5">
<PrivateAssets>all</PrivateAssets>
<IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
</PackageReference>
</ItemGroup>
<ItemGroup>
<Using Include="Xunit" />
</ItemGroup>
</Project>P.S.: The fact that it fails around 79-80 is funny.
Expected behavior
Be should throw only XunitException for string comparisons - strings are either equal or not equal.
IMHO, building final assertion message incrementally using multiple string.Format calls feels too hacky.
Probably, a better approach would be to create some tree-ish type and walking over it to build the final string. But I'm not regularly programming in C# so don't listen to me. :)
Actual behavior
In reproduction tests:
- The
NotOktest fails - the actual string is "{" and then 80+ "x"s and it is compared to an empty string. - The
Oktest succeeds but it has string.Format error in the assertion message - the actual string is "{" and 79 "x"s.
Full dotnet test result:
PS C:\MY\NotWork\UpdateAlWorkspaceThing> dotnet test
Restore complete (0,5s)
UpdateAlWorkspaceThing.Tests net10.0 succeeded (0,1s) → UpdateAlWorkspaceThing.Tests\bin\Debug\net10.0\UpdateAlWorkspaceThing.Tests.dll
[xUnit.net 00:00:00.00] xUnit.net VSTest Adapter v3.1.5+1b188a7b0a (64-bit .NET 10.0.2)
[xUnit.net 00:00:00.05] Discovering: UpdateAlWorkspaceThing.Tests
[xUnit.net 00:00:00.08] Discovered: UpdateAlWorkspaceThing.Tests
[xUnit.net 00:00:00.10] Starting: UpdateAlWorkspaceThing.Tests
Warning:
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[xUnit.net 00:00:00.15] UpdateAlWorkspaceThing.Tests.DemonCoreTests.NotOk [FAIL]
[xUnit.net 00:00:00.15] Expected a <Xunit.Sdk.XunitException> to be thrown, but found <System.FormatException>:
[xUnit.net 00:00:00.15] System.FormatException: Input string was not in a correct format. Failure to parse near offset 59. Expected an ASCII digit.
[xUnit.net 00:00:00.15] at System.Text.StringBuilder.AppendFormat(IFormatProvider provider, String format, ReadOnlySpan`1 args)
[xUnit.net 00:00:00.15] at System.Text.StringBuilder.AppendFormat(IFormatProvider provider, String format, Object[] args)
[xUnit.net 00:00:00.15] at FluentAssertions.Primitives.StringEqualityStrategy.GetMismatchSegmentForLongStrings(String subject, String expected, Int32 firstIndexOfMismatch)
[xUnit.net 00:00:00.15] at FluentAssertions.Primitives.StringEqualityStrategy.AssertForEquality(AssertionChain assertionChain, String subject, String expected)
[xUnit.net 00:00:00.15] at FluentAssertions.Primitives.StringValidator.Validate(String subject, String expected)
[xUnit.net 00:00:00.15] at FluentAssertions.Primitives.StringAssertions`1.Be(String expected, String because, Object[] becauseArgs)
[xUnit.net 00:00:00.15] at UpdateAlWorkspaceThing.Tests.DemonCoreTests.<>c__DisplayClass2_0.<DemonCore>b__0() in C:\MY\NotWork\UpdateAlWorkspaceThing\UpdateAlWorkspaceThing.Tests\CustomFormatterTests.cs:line 25
[xUnit.net 00:00:00.15] at FluentAssertions.Specialized.ActionAssertions.InvokeSubject()
[xUnit.net 00:00:00.15] at FluentAssertions.Specialized.DelegateAssertions`2.InvokeSubjectWithInterception().
[xUnit.net 00:00:00.15] Stack Trace:
[xUnit.net 00:00:00.16] at FluentAssertions.Execution.LateBoundTestFramework.Throw(String message)
[xUnit.net 00:00:00.16] at FluentAssertions.Execution.DefaultAssertionStrategy.HandleFailure(String message)
[xUnit.net 00:00:00.16] at FluentAssertions.Execution.AssertionScope.AddPreFormattedFailure(String formattedFailureMessage)
[xUnit.net 00:00:00.16] at FluentAssertions.Execution.AssertionChain.FailWith(Func`1 getFailureReason)
[xUnit.net 00:00:00.16] at FluentAssertions.Execution.AssertionChain.FailWith(Func`1 getFailureReason)
[xUnit.net 00:00:00.16] at FluentAssertions.Execution.AssertionChain.FailWith(String message, Object[] args)
[xUnit.net 00:00:00.16] at FluentAssertions.Specialized.DelegateAssertionsBase`2.<>c__DisplayClass8_0`1.<ThrowInternal>b__0(AssertionChain chain)
[xUnit.net 00:00:00.16] at FluentAssertions.Execution.AssertionChain.WithExpectation(String message, Action`1 chain, Object[] args)
[xUnit.net 00:00:00.16] at FluentAssertions.Execution.AssertionChain.WithExpectation(String message, Object arg1, Action`1 chain)
[xUnit.net 00:00:00.16] at FluentAssertions.Specialized.DelegateAssertionsBase`2.ThrowInternal[TException](Exception exception, String because, Object[] becauseArgs)
[xUnit.net 00:00:00.16] at FluentAssertions.Specialized.DelegateAssertions`2.Throw[TException](String because, Object[] becauseArgs)
[xUnit.net 00:00:00.16] C:\MY\NotWork\UpdateAlWorkspaceThing\UpdateAlWorkspaceThing.Tests\CustomFormatterTests.cs(11,0): at UpdateAlWorkspaceThing.Tests.DemonCoreTests.NotOk()
[xUnit.net 00:00:00.16] at System.Reflection.MethodBaseInvoker.InterpretedInvoke_Method(Object obj, IntPtr* args)
[xUnit.net 00:00:00.16] at System.Reflection.MethodBaseInvoker.InvokeWithNoArgs(Object obj, BindingFlags invokeAttr)
[xUnit.net 00:00:00.16] Finished: UpdateAlWorkspaceThing.Tests
UpdateAlWorkspaceThing.Tests test net10.0 failed with 1 error(s) (0,7s)
C:\MY\NotWork\UpdateAlWorkspaceThing\UpdateAlWorkspaceThing.Tests\CustomFormatterTests.cs(11): error TESTERROR:
UpdateAlWorkspaceThing.Tests.DemonCoreTests.NotOk (6ms): Error Message: Expected a <Xunit.Sdk.XunitException> to be thrown, but found <System.FormatExcep
tion>:
System.FormatException: Input string was not in a correct format. Failure to parse near offset 59. Expected an ASCII digit.
at System.Text.StringBuilder.AppendFormat(IFormatProvider provider, String format, ReadOnlySpan`1 args)
at System.Text.StringBuilder.AppendFormat(IFormatProvider provider, String format, Object[] args)
at FluentAssertions.Primitives.StringEqualityStrategy.GetMismatchSegmentForLongStrings(String subject, String expected, Int32 firstIndexOfMismatch)
at FluentAssertions.Primitives.StringEqualityStrategy.AssertForEquality(AssertionChain assertionChain, String subject, String expected)
at FluentAssertions.Primitives.StringValidator.Validate(String subject, String expected)
at FluentAssertions.Primitives.StringAssertions`1.Be(String expected, String because, Object[] becauseArgs)
at UpdateAlWorkspaceThing.Tests.DemonCoreTests.<>c__DisplayClass2_0.<DemonCore>b__0() in C:\MY\NotWork\UpdateAlWorkspaceThing\UpdateAlWorkspaceThing.T
ests\CustomFormatterTests.cs:line 25
at FluentAssertions.Specialized.ActionAssertions.InvokeSubject()
at FluentAssertions.Specialized.DelegateAssertions`2.InvokeSubjectWithInterception().
Stack Trace:
at FluentAssertions.Execution.LateBoundTestFramework.Throw(String message)
at FluentAssertions.Execution.DefaultAssertionStrategy.HandleFailure(String message)
at FluentAssertions.Execution.AssertionScope.AddPreFormattedFailure(String formattedFailureMessage)
at FluentAssertions.Execution.AssertionChain.FailWith(Func`1 getFailureReason)
at FluentAssertions.Execution.AssertionChain.FailWith(Func`1 getFailureReason)
at FluentAssertions.Execution.AssertionChain.FailWith(String message, Object[] args)
at FluentAssertions.Specialized.DelegateAssertionsBase`2.<>c__DisplayClass8_0`1.<ThrowInternal>b__0(AssertionChain chain)
at FluentAssertions.Execution.AssertionChain.WithExpectation(String message, Action`1 chain, Object[] args)
at FluentAssertions.Execution.AssertionChain.WithExpectation(String message, Object arg1, Action`1 chain)
at FluentAssertions.Specialized.DelegateAssertionsBase`2.ThrowInternal[TException](Exception exception, String because, Object[] becauseArgs)
at FluentAssertions.Specialized.DelegateAssertions`2.Throw[TException](String because, Object[] becauseArgs)
at UpdateAlWorkspaceThing.Tests.DemonCoreTests.NotOk() in C:\MY\NotWork\UpdateAlWorkspaceThing\UpdateAlWorkspaceThing.Tests\CustomFormatterTests.cs:li
ne 11
at System.Reflection.MethodBaseInvoker.InterpretedInvoke_Method(Object obj, IntPtr* args)
at System.Reflection.MethodBaseInvoker.InvokeWithNoArgs(Object obj, BindingFlags invokeAttr)
Test summary: total: 2; failed: 1; succeeded: 1; skipped: 0; duration: 0,7s
Build failed with 1 error(s) in 1,5sRegression?
Partial - downgrading to 8.7.0 makes both tests pass, but it still has the string.Format error in the assertion message:
**WARNING** failure message 'Expected actual to be the same string, but they differ at index 0:
↓ (actual)
"{xxxxxxxxxxxxxxxxxxx…"
""
↑ (expected).' could not be formatted with string.Format
at System.Text.ValueStringBuilder.AppendFormatHelper(IFormatProvider provider, String format, ReadOnlySpan`1 args)
at System.String.FormatHelper(IFormatProvider provider, String format, ReadOnlySpan`1 args)
at System.String.Format(IFormatProvider provider, String format, Object[] args)
at FluentAssertions.Execution.FailureMessageFormatter.FormatArgumentPlaceholders(String failureMessage, Object[] failureArgs)
The goal is not to make exception disappear. It is to fix the incorrect behavior.
Known Workarounds
Replacing "{" with "{{" before comparing.
Configuration
- FluentAssertions v8.8.0
- .NET 10.0
Other information
No response
Are you willing to help with a pull-request?
No